1. Field of the Invention
This invention pertains to the field of single-component, moisture-curing, polyurethane systems for use in coatings, adhesives, and similar applications. The systems contain a polyurethane prepolymer, certain dialdimines, and certain acid catalysts.
2. Description of the Prior Art
The use of moisture-sensitive amine derivatives such as aldimines and ketimines as latent hardeners for polyisocyanates is known. In the presence of moisture, the aforementioned amine derivatives form free amines which react with the polyisocyanates by forming urea and biuret groups.
Polyaldimines and polyketimines as well as their use as mixtures with polyisocyanates are described, for instance, in British Pat. Nos. 1,064,841 and 1,073,209, U.S. Pat. Nos. 3,493,543 and 3,523,925 and French Pat. No. 1,493,879 (British Pat. No. 1,125,836). In most cases, however, the storage stability of the mentioned compounds is unsatisfactory.
While the products described in German Application No. 21 25 247 and German Published Application No. 26 51 479 (British Pat. No. 1,575,666) show improvements compared with the compounds according to the then existing state of the art, their storage stability, particularly in the presence of acid, is still insufficient for application in single-component polyurethane systems.